Apparatus for manipulating crystal morphology to achieve stable fluidization

ABSTRACT

This disclosure provides an apparatus to manipulate the crystal morphology of a powder to improve the flow of a powder from a vessel and/or flowability of a powder in order to achieve stable fluidization of the powder within a vessel.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of U.S. application Ser.No. 17/173,645, filed Feb. 11, 2021 now abandoned, which claims thebenefit of U.S. application Ser. No. 16/421,575, now U.S. Pat. No.10,988,960, filed May 24, 2019, which claims the benefit of U.S.Provisional Application Ser. No. 62/679,428, filed Jun. 1, 2018. Thedisclosures of the prior application are considered part of (and areincorporated by reference in) the disclosure of this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to material handling, more particularly,to improving the fluidization (flow) of a material, providing advantagesin functionality, simplicity and engineering, operation, maintenance,and life cycle cost. The invention can be utilized in a dry scrubbersystem utilizing Dry Sorbent Injection (DSI). However, the invention isnot limited to this application.

2. Description of the Related Art

It is well known among those who work in the area of material handlingthat material containing a high percentage of solids can be difficult toremove from a storage vessel. The foremost view in the art is that ahigh unconfined yield strength is primarily responsible for flow issuesin storage vessels, for example arching, rat-holing, and bridging.¹Unconfined yield strength is the major requisite stress to cause a groupof particles to “yield,” which results in shear movement of the bulkmaterial (this is related to resistance to flow).² ¹ Johanson, Kerry,Effect of particle shape on unconfined yield strength, PowderTechnology, Vol. 194, 2009, 246-251, Elsevier B.V.² Johanson, Kerry,Effect of particle shape on unconfined yield strength, PowderTechnology, Vol. 194, 2009, 246-251, Elsevier B.V.

A further leading view is that any moisture in the material will tend tocongregate at the contact points between soluble particles, causing aportion of the particles to dissolve.³ If the temperature thenincreases, the theory is, this moisture between particles evaporates,leaving solid salt bridges between adjacent particles. These saltbridges increase the adhesive force on the particles and therefore theunconfined yield strength as well, impeding fluidization. Therefore, thetheory is, as temperature increases, flowability deteriorates. ³Johanson, Kerry, Powder Pointers, Summer 2018 Volume 12 No B, MaterialFlow Solutions, Inc, 1-2, Gainesville, Fla.

U.S. Pat. No. 4,061,246 teaches one of ordinary skill in the art to: 1.use an orbital feed plate, 2. avoid fluidization in the vicinity of anoutlet portal, and 3. position an aeration device above the outletportal and bottom of the vessel. The present invention does not requireand therefore overcomes these elements and limitations.

BRIEF SUMMARY OF THE INVENTION

It is an object of this disclosure to describe the experimentation whichilluminated that the crystal structure of a material impactsfluidization, resulting in improved flowability at higher temperaturesdespite the common belief otherwise. It is an object of the presentinvention to provide a system and method for achieving stablefluidization of a powder comprising materials, such as sodium sulfate,with crystal morphology that can be manipulated with temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure andtogether with the description serve to explain the principles of thedisclosure. In the drawings:

FIG. 1 shows a typical fluidization profile used to determine air flow(pressure) requirements for fluidizing particles.

FIG. 2 shows experimental data, unconfined yield strength as a functionof temperature.

FIG. 3 shows moisture vs. temperature experimental data.

FIG. 4 shows additional moisture and temperature experimental data overtime.

FIG. 5 shows a solubility curve of sodium sulfate in solution.

FIG. 6 shows an example of crystals with an orthorhombic morphology withtwinning planes.

FIG. 7 shows an example of crystals with a monoclinic morphology, and notwinning planes.

FIG. 8 shows an example of crystals with a hexagonal morphology, and notwinning planes.

FIG. 9 shows an example embodiment of sodium sulfate collection andtransport, representing an application of the present disclosure inrelation to the use of Dry Sorbent Injection in a coal-fired powerplant.

FIG. 10 shows a storage vessel, for example a silo, truck, trailer, orrail car, and the accompanying system for improving flowability andachieving stable fluidization according to an example embodiment of thepresent disclosure.

FIG. 11 shows a gas stream distribution system including an aerationdevice for improving flowability and achieving stable fluidizationaccording to an example embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

It is well known among those who work in the area of material handlingthat material containing a high percentage of solids can be difficult toremove from a storage vessel. The foremost view in the art is that ahigh unconfined yield strength is primarily responsible for flow issuesin storage vessels.⁴ ⁴ Johanson, Kerry, Powder Pointers, Summer 2018Volume 12 No B, Material Flow Solutions, Inc, 1-2, Gainesville, Fla.

A further leading view is that any moisture in the material will tend tocongregate at the contact points between particles, causing the portionof the soluble particles near these contact points to dissolve.⁵ Theleading theory is that if temperature is increased, this moisturebetween particles evaporates, leaving solid salt bridges betweenadjacent particles. These salt bridges increase the adhesive force onthe particles and therefore the unconfined yield strength as well,impeding powder flow. Therefore, the theory is, as temperatureincreases, flowability deteriorates. ⁵ Johanson, Kerry, Powder Pointers,Summer 2018 Volume 12 No B, Material Flow Solutions, Inc, 1-2,Gainesville, Fla.

Despite the view among prominent members in the art to the contrary,both laboratory and field testing indicate that material flow problemsare not necessarily due to moles of hydration or free water, and do notnecessarily increase with temperature. Rather, the crystalline structureof a compound influences powder flowability.

For example, the crystal morphology (otherwise known as crystalstructure) of anhydrous sodium sulfate at ordinary temperatures (belowabout 100 degrees C.) is an orthorhombic pyramidal crystal with twinningplanes.⁶ A twin is defined as a composite crystal built from two or morecrystal specimens that are grown together in a specific manner so thatthere is at least one plane and a direction perpendicular to it that arerelated in the same manner to the crystallographic axes of both parts ofthe twin.⁷ But at temperatures greater than and equal to about 100degrees C. (212 degrees F.), the crystal shape changes to a monocliniccrystal (without twinning) and then at about 250 degrees C. (482 degreesF.) to hexagonal crystals (without twinning).⁸ The lack of twinning inthe crystal morphology results in the achievement of stable fluidizationat and beyond about 100 degrees C., versus the failure to achieve stablefluidization, or even fluidization, below about 100 degrees C. Twinnedcrystals experience a greater unconfined yield strength because of thephysical interlocking that occurs between particles due to the shape ofthe twinned crystals. It has been shown that particle shape as well asthe number of contact points per adjacent particle affect unconfinedyield strength and therefore flowability.⁹ Experimental Methods ⁶ TheColumbia Encyclopedia, 2000, 2646, 6^(th) Edition, Gale Group, U.S.⁷Glusker, Jenny P, Trueblood, Kenneth N., Crystal Structure Analysis: APrimer, 1985, 240, Oxford University Press, New York.⁸ The ColumbiaEncyclopedia, 2000, 2646, 6^(th) Edition, Gale Group, U.S.⁹ Johanson,Kerry, Effect of particle shape on unconfined yield strength, PowderTechnology, Vol. 194, 2009, 246-251, Elsevier B.V.

Contrary to the popular belief that flowability deteriorates withincreasing temperature, experimental data showed that flowabilityimproved at higher temperatures, even to the point of achieving stableof fluidization. Fluidization is readily determined via a visualinspection of a column of material aerated with air. The air flow ismeasured and recorded, from which air velocities are calculated. Thetemperature of heated air is measured with a thermocouple or othertemperature measuring device. If unheated, the air is assumed to be atambient temperature, near 25 degrees C. (77 degrees F.).

If the column of material forms fissures (small, visible tunnels throughthe material) that provide a multitude of visible conduits for the airto pass through the material and relieve the built up pressure beneaththe material, then the material is said to be experiencing fissures, orchanneling, and has not reached fluidization.¹⁰ ¹¹ ¹⁰ Cocco, R. et. al.,Introduction to Fluidization, November 2014, 21-29, American Instituteof Chemical Engineers Journal, U.S.¹¹ Vasconcelos, P. S., AmaranteMesquita, A. L., Minimum and Full Fluidization Velocity for Alumina Usedin the Aluminum Smelter, November 2011, 8-13, Volume 3 No. 4,International Journal of Engineering Business Management, Intech OpenAccess Publisher.

Alternatively, if the column of material allows distinct volumes of airto be relieved periodically and in an uneven manner, the material issaid to be experiencing bubbling flow, and it is not consistentlyfluidized.¹² ¹³ ¹² Cocco, R. et. al., Introduction to Fluidization,November 2014, 21-29, American Institute of Chemical Engineers Journal,U.S.¹³ Vasconcelos, P. S., Amarante Mesquita, A. L., Minimum and FullFluidization Velocity for Alumina Used in the Aluminum Smelter, November2011, 8-13, Volume 3 No. 4, International Journal of EngineeringBusiness Management, Intech Open Access Publisher.

However, if air passes uniformly through the material causing thematerial to uniformly expand and behave in a fluid-like manner, thematerial is said to have achieved stable fluidization.¹⁴ ¹⁵ ¹⁴ Cocco, R.et. al., Introduction to Fluidization, November 2014, 21-29, AmericanInstitute of Chemical Engineers Journal, U.S.¹⁵ Vasconcelos, P. S.,Amarante Mesquita, A. L., Minimum and Full Fluidization Velocity forAlumina Used in the Aluminum Smelter, November 2011, 8-13, Volume 3 No.4, International Journal of Engineering Business Management, Intech OpenAccess Publisher.

The experiment comprised a vessel with sufficient sodium sulfate powderto form a bed of material within the vessel. The vessel was configuredto allow air, either heated or unheated, to be introduced below thematerial. The temperature of the ambient air was recorded at 25 degreesC. (77 degrees F.). This is assumed to be the approximate temperature ofthe desiccated aeration air and thus of the sodium sulfate powder whenunheated.

First, at ambient temperature, flow (pressure) was increased untilfissures were observed through the material to the surface, relievingitself into the room. Pressure was increased gradually until the flowrate of the desiccated air was more than twenty times what is typicallyneeded for fluidization. The material gradually transitioned intobubbling flow, but fluidization was never achieved.

The test apparatus was then modified for higher temperatures. Desiccatedair at no less than 107 degrees C. (225 degrees F.) was introduced intothe now insulated apparatus to prompt aeration. The desiccated air waspermitted to run overnight prior to visual observation to ensure thatthe apparatus itself, as well as the powder in the apparatus, weresufficiently heated above the transition temperature. The material wasobserved to be stably fluidized though observation points cut into theinsulation.

To confirm fluidization, the desiccated aeration air was brieflyterminated, upon which the column of material dropped slowly to a lesservolume. Once this contraction was complete and the desiccated aerationair again initiated, the material uniformly increased in volume and thedesiccated aeration air passed through the material with no visiblefissures, channels, or bubbling. The material achieved stablefluidization. The test was continued by allowing the material to coolbelow about 100 degrees C., and fluidization was lost. Only thetemperature of the desiccated air was changed, meaning the fluidizationthat occurred above 100 degrees C. and which ceased below thattemperature could not have been due to another variable such asmoisture. Likewise, upon reheating to about 107 degrees C. (225 degreesF.), fluidization was again achieved.

The ultimate fluidization test was conducted in the field. The fieldsetup was similar to that in the lab except the silo was not insulateddue to the sufficient outside temperature, and the source of air in thefield was ambient air versus desiccated air in the lab. The temperatureof the gas stream reached 225 degrees F. (about 107 degrees C.) for aperiod of several days. Stable fluidization under these conditions wasachieved, as evidenced by the silo being readily emptied.

The amount of air required for fluidization is dependent on thematerial. A typical fluidization profile is depicted in FIG. 1 .¹⁶Fluidization of a powder is achieved when the powder volume increasesuniformly and the resultant powder flow characteristics approach that ofa fluid. This point, fluidization, is identified as the “MinimumFluidization Velocity” (1). As velocity increases further, there is adistinct reduction in the pressure drop (Δp) across the powder (2), andthen as the velocity increases further, pressure drop (Δp) becomesstable at the minimum operating velocity (3). Minimum operating velocity(3), or stable fluidization, is judged to be reached where perturbationsin air flow or back pressure avoid significant changes in pressure dropsand thus do not impact the overall fluidization of the bulk powder. Themaximum operating velocity (4) must be low enough to avoid the velocitywhere entrainment occurs (5). The operating velocity range for stablefluidization must be great enough to reach the point at which thepressure drop decreases and becomes stable (3), and less than thevelocity which induces entrainment (5). ¹⁶ Kunii, Daizo and Levenspiel,Octave, Fludization Engineering, 1969, 74, John Wiley & Sons, Inc., U.S.

In the experimentation completed, the minimum operating velocity andvolume for stable fluidization was calculated to be sufficient toachieve proper fluidization. The specific values are proprietary, butthe velocity and flow rate applied were four times the calculated value.Despite vastly exceeding the calculated volume of air introduced to thepowder bed via the aeration device according to the above methodology,the material never achieved fluidization at temperatures below about 100degrees C.

During laboratory testing above the aforementioned transitiontemperature of about 100 degrees C. (212 degrees F.), stablefluidization was achieved at velocities and flow rates very close to thecalculated values, disproving the common belief in the art that theunconfined yield strength, and therefore flow issues as well, of solublepowders such as sodium sulfate increase with temperature.

FIG. 2 shows a trend line of unconfined yield strength versustemperature applied to experimental data, illustrating the common viewin the art that unconfined yield strength increases with temperature.This indicates the expectation that unconfined yield strength wouldincrease beyond 100 degrees C. and therefore flowability would continueto deteriorate.

Contrary to this common view, the lab data showed fluidization occurredbeyond about 100 degrees C., therefore unconfined yield strength mustdramatically drop. Note that no data was collected above 100 degrees C.(212 degrees F.), yet the trend line from the data extends beyond 100degrees C. Those knowledgeable in the art who created the graph assumedthe relationship was linear, and extended the trend line beyond 100degrees C. However, as this disclosure elucidates, lower unconfinedyield strength and therefore less flow issues, not a higher unconfinedyield strength and more flow issues, are present beyond 100 degrees C.,and an accurate graph would show a negative slope beyond 100 degrees C.

Based on this trend line, the temperatures in the field were reducedfrom their initial temperatures of about 93 degrees C. (about 200degrees F.) to about 71 degrees C. (160 degrees F.). There were nomeasureable improvements to the flow of the material out of the silodespite this reduction in temperature.

Additionally, an analysis was completed of the moisture content of thesilo powder at various temperatures to determine if the loss in moistureat 100 degrees C. (212 degrees F.) is the reason for its ability tofluidize. This analysis disproved the theory that flow improved to thepoint of allowing stable fluidization because of the loss of free waterfrom the sodium sulfate powder. In fact, moisture data indicates thatmost of the free moisture is liberated at temperatures below 100 C (212F), pointing to an alternate cause for the dramatic change in flowcharacteristics of sodium sulfate powder above 100 degrees C. comparedto below 100 degrees C.

FIG. 3 presents the released moisture from a powder sample as a functionof temperature in light of the above. Note that the powder was tested attemperatures of up to about 215 degrees F. (102 degrees C.). It shows nodramatic change in moisture released at the transition temperature of212 degrees F., meaning moisture content is not determinative.

Similarly, FIG. 4 presents the relationship of moisture released as afunction of both powder temperature and elapsed time. At 50 degrees C.(122 degrees F.), the moisture released is 1.2% by weight (mass). Whenthis temperature is raised to 100 degrees C. (212 degrees F.), themoisture release increases from 1.2% to 1.9%, for a net increase of0.7%. When the transition temperature is exceeded at the third point,150 degrees C. (302 degrees F.), the moisture released increases from1.9% to 2.0% for a net increase of 0.10% moisture. It is interesting tonote that when the transition temperature of 100 degrees C. (212 degreesF.) is exceeded, the increase in moisture release is only 0.10%. Thisshould be juxtaposed with the 0.7% increase from 50 to 100 degrees C.(where no transition temperature was exceeded) or the 1.2% increase fromambient temperature to 50 degrees C. This lack of dramatic change,hardly any in fact, suggests that moisture content in the powder is notthe primary reason for the inability to fluidize. Desiccation of theaeration air minimized the chances of introducing additional moistureinto the test apparatus or sodium sulfate powder. The above resultseliminate moisture in the sodium sulfate powder as a major contributingfactor to the fluidization of the powder.

Although the theoretical transition temperature is 100 degrees C. (212degrees F.), it should be understood that due to, for example theimpurities in the mixture, the exact point of transition may be slightlydifferent than the published value. Nonetheless, it is interesting tonote that there is no dramatic increase, only a net increase of 0.10%,in measured moisture release when crossing the transition temperature of100 degrees C. (212 degrees F.).

Considering the crystal structure of sodium sulfate, as well as itschemical transition temperature, sheds further light on the lack offluidization below the aforementioned transition temperature. Sodiumsulfate has a low-end chemical transition temperature of about 32degrees C. (90 degrees F.),¹⁷ as shown in FIG. 5 .¹⁸ FIG. 5 shows sodiumsulfate in solution, illustrating that a chemical change occurs withtemperature (the morphology transition temperatures were approximated asthey were not yet established). ¹⁷ Dickinson, H. C.; Mueller, E. F., Thetransition temperature of sodium sulfate referred anew to theinternational standard, 1907, 1381, 29 Journal of the American ChemicalSociety.¹⁸ Garrett, Donald E., Sodium Sulfate: Handbook of Deposits,Processing, Properties, and Use, 2001, 346, Academic Press, U.S.

At room temperature, sodium sulfate assumes an orthorhombic crystallinestructure, while above about 100 degrees C. (212 degrees F.) it assumesa monoclinic structure, and above about 250 degrees C. (482 degrees F.)it assumes a hexagonal structure.¹⁹ Other sources identify thecrystalline structure at ambient temperatures to be orthorhombic²⁰ ororthorhombic pyramidal.²¹ ¹⁹ The Columbia Encyclopedia, 2000, 2646,6^(th) Edition, Gale Group, U.S.²⁰ Wyckoff, R. W. G., The Structure ofCrystals, Second Edition, 1935, 66, Reinhold Publishing Corporation, NewYork, U.S.²¹ Garrett, Donald E., Sodium Sulfate: Handbook of Deposits,Processing, Properties, and Use, 2001, 346, Academic Press, U.S.

A 1923 USGS report further describes sodium sulfate crystals at ambienttemperature as orthorhombic crystals exhibiting twinning.²² Thecrystalline structure for anhydrous sodium sulfate is an orthorhombicpyramidal crystal with twinning planes as shown in FIG. 6 .²³ At 100degrees C. (212 degrees F.) the crystal shape changes to a monocliniccrystal, shown in FIG. 7 . A comparison of FIG. 6 and FIG. 7 illustratesthat the morphology resulting from the twinning in the orthorhombiccrystals makes it more difficult for the powder to achieve stablefluidization due the potential for the powder's twinning planes tointerlock resulting in a higher yield strength of the powder. ²² Wells,Roger C., Sodium Sulfate: Its Sources and Uses, Bulletin 717, Departmentof the Interior, United States Geological Survey, 2-3.²³ Wells, RogerC., Sodium Sulfate: Its Sources and Uses, Bulletin 717, Department ofthe Interior, United States Geological Survey, 2-3.

The next aforementioned transition temperature is at 250 degrees C. (482degrees F.), well above the temperature range relevant to thisdiscussion.²⁴ However beginning at this transition, the morphology ofsodium sulfate transforms to hexagonal crystals as shown in FIG. 8 ,without twinning, and thus fluidization can be achieved as with themonoclinic crystals. ²⁴ Wells, Roger C., Sodium Sulfate: Its Sources andUses, Bulletin 717, Department of the Interior, United States GeologicalSurvey, 2-3.

TABLE 1 Table of crystalline structure of anhydrous sodium sulfate atvarious transition temperatures Anhydrous Sodium Sulfate TemperaturesCrystalline Structure Room Temperature, Orthorhombic Pyramidal 21degrees C. (70 degrees F.) Crystal with Twinning Planes 100 degrees C.(212 degrees F.) Monoclinic Crystal 250 degrees C. (482 degrees F.)Hexagonal Crystal

X-ray diffraction (XRD) was performed on a sample of powder from thesilo, but the results were not meaningful. Later, this failure to obtainmeaningful XRD results was attributed to the presence of twinningcrystals. XRD is unable to identify crystalline structures when twinningis present.²⁵ ²⁶ This limitation on one of the primary methods toidentify crystalline structures may explain why most sources fail toidentify twinning as a common structure for sodium sulfate. In fact,some even recommend avoiding conducting an XRD on crystals exhibitingtwinning, or to modify the crystal to exclude twinning.²⁷ ²⁵ PickworthGlusker, J., Trueblood, K. N., Crystal Structure Analysis, A Primer,1985, 191-194, Second Edition, Oxford University Press.²⁶ U.S. Pat. No.7,696,991B2, Apr. 13, 2010, Higashi, [0004].²⁷ Glusker, Jenny P,Trueblood, Kenneth N., Crystal Structure Analysis: A Primer, 1985, 194,Oxford University Press, New York.

INVENTION DISCLOSED

Dry Sorbent Injection (DSI) is an example application of the disclosureherein. Though not part of the claimed invention, a discussion of DSI isincluded in this disclosure (FIG. 9 ) for clarity. DSI is a viableoption for air quality control. It achieves mitigation of SO₂ and otheracid gasses at relatively low capital costs, making it an attractiveretrofit option. As this technology is implemented on a large (e.g.power plant) scale, flow issues can arise with the powder beingcollected.

In DSI as shown in FIG. 9 , sodium bicarbonate (SBC) (7) is injected inorder to react with acid gasses such as SO₂, for example in a coal-firedpower plant's flue gas (6), downstream or upstream of an optionalelectrostatic precipitator (8) and upstream of fabric bags in a pulsejet fabric filter (PJFF) (9) with hoppers (12) insulated as necessary.After injection, the SBC (7) calcines due to higher temperatures to makeNa₂CO₃, and the SO₂ gas and Na₂CO₃ react to produce sodium sulfate asexpressed in Equations 1 and 2, below.2NaHCO₃+Heat□Na₂CO₃+H₂O (g)  Eq. 1:Na₂CO₃+SO₂+½O₂→Na₂SO₄+CO₂ (g)  Eq. 2:

A powder (11) entrained in flue gas (6) is collected by fabric bags inPJFF (9), shed to insulated inverted pyramidal hoppers (12), and throughan airlock (13) to a pneumatic conveying line of a heated gas stream(14), which can be of motive ambient air (15) and which is mobilized,for example with a blower (16). Pneumatic conveying line of heated gasstream (14) has a pressure relief valve (17) to eliminate any excesspressure, and is conveyed for example by a conduit (18), and heated witha temperature control means such as an electric heater (19). Thetemperature of the ambient air (15) is measured by a temperature sensor,for example a thermocouple (21), which is sent to a temperature controlmeans (20), and this temperature is compared to a first set pointtemperature. If the temperature is lower than the first set pointtemperature, the temperature control means (20) sends a signal toenergize heater (19), to heat the ambient air (15) to at least the firstset point temperature.

Pneumatic conveying line of a heated gas stream (14) pneumaticallytransports powder (11) to a vessel (34) as shown in FIG. 10 . Flue gas(6) is exhausted at location (10), eventually to the environment.

Powder (11), used to illustrate the preferred embodiment is mainlysodium sulfate (greater than about 98%) combined with impurities, whichare in the present disclosure as a small amount of fly ash (less thanabout 1%) and activated carbon (less than about 1%) depending on theamount of mercury in the fuel, but can be these materials in otheramounts or other materials. An issue occurs when the silo will notdischarge the powder effectively into a disposal container, for example,in the application of DSI. The present invention comprises an apparatusand method for manipulating crystal structure of a powder in order toachieve stable fluidization. Embodiments of the present invention willnow be described in detail with reference to the drawings.

A preferred embodiment of the invention is shown in FIG. 10 . FIG. 10shows a storage vessel (34) such as a truck, trailer, rail car, or as inthe present embodiment, a silo, and the accompanying system forachieving stable fluidization according to an example embodiment of thepresent disclosure.

Vessel (34) has a rigid exterior shell (30), and collects powder (11)for disposal, forming powder bed (24). The silo of the preferredembodiment has a flat bottom but the vessel is not limited to having aflat bottom. The disclosure herein allows for the achievement of stablefluidization in silos with flat bottoms, thereby avoiding the additionalcosts associated with silos with conical bottoms.

As shown in FIG. 10 , vessel (34) has a rigid exterior shell (30) whichcan have insulation (31), has an inlet portal (22) through which powder(11) enters into an interior space (23) in the silo forming powder bed(24). Vessel (34) also comprises at least one atmospheric vent (33)which can be a bin vent filter with an optional exhaust fan, extendingfrom interior space (23) through exterior shell of the vessel (30).

A gas stream (43) is introduced to interior space (23) of vessel (34)and powder bed (24) therein via at least one gas inlet connection (25)and an aeration device (29). Aeration device (29) can be, but is notlimited to, air slides, pads, or pozzolanic stones. Aeration device (29)can further comprise a mesh, cloth, felt, or other fabric (woven orunwoven) that covers the air slides, pads, or other pozzolanic stones,and provides a medium to evenly distribute the heated gas across thearea of the air slides, pads, or stones and is designed for a uniformgas velocity determined to be sufficient for fluidization. Oncefluidized, the powder exits the silo via an outlet portal (32). Theaeration device (29) is positioned below the outlet portal (32). In oneembodiment of the present invention, aeration device (29) is positionedso as to be in contact with the bottom of interior space (23) of vessel(34), below outlet portal (32). In another embodiment of the presentinvention, aeration device (29) is suspended above the bottom ofinterior space (23) of vessel (34), below outlet portal (32).

Gas stream (43) heats powder bed (24). The temperature of powder bed(24) is measured by a temperature sensor (26), for example athermocouple that in the preferred embodiment extends from the exteriorof the vessel (30) to interior space (23). Powder bed (24) is heated toat least a first predetermined transition temperature, which in thepresent embodiment is about 100 degrees C. for sodium sulfate. Thiscontrols the crystal structure such that twinning is eliminated, andcombined with the motive force imparted by gas stream (43) via aerationdevice (29), powder bed (24) achieves stable fluidization. Gas stream(43) exits via atmospheric vent (33) and powder (11), now fluidized,exits the vessel via an outlet portal (32).

Gas stream (43) is also pressurized and controlled by a pressure controldevice such as a control or throttling valve (28) to establish a gasstream flow rate sufficient to achieve initial fluidization of powderbed (24). A pressure indicator (27) (for example, a pressure gauge) maybe used to determine when to adjust the air pressure to establish stablefluidization which is defined further in FIG. 1 .

The preferred embodiment shown in FIG. 11 utilizes gas streamdistribution system (100). Gas stream (43) is controlled to maintain atleast a first predetermined transition temperature selected so that thepowder (11) lacks twinning.

A temperature sensor (26), for example a thermocouple, measures thetemperature of powder bed (24). The temperature of powder bed (24) issent to a temperature control means (42), and this temperature iscompared to the first predetermined transition temperature. If thetemperature of powder bed (24) is lower than the first predeterminedtransition temperature, temperature control means (42) sends a signal toenergize a heating device (39) to heat gas stream (43) to at least thefirst predetermined transition temperature. Temperature sensor (26) canbe located elsewhere in gas stream (43) as long as it is downstream ofheating device (39).

As described above, gas stream (43) is also pressurized and controlledby pressure control device such as a control or throttling valve (28) toestablish a gas stream flow rate sufficient to achieve initialfluidization of the powder bed. Pressure indicator (27) (for example, apressure gauge) may be used to determine when to adjust the air pressureto establish stable fluidization, which is defined further in FIG. 1 . Apressure relief valve (37) allows excess pressure to be released fromthe system.

The gas stream (43) must overcome a first resistance to the gas streamflow inherent in gas stream distribution system (100). It must alsoovercome a second resistance to gas flow resulting from the structure ofpowder bed (24), wherein after achieving initial fluidization of thepowder bed, the flow rate of gas stream (43) is further adjusted toachieve stable fluidization of powder bed (24) without causing powder(11) to become entrained in gas stream (43).

Gas stream distribution system (100) further comprises heater (39) andmobilization means (36) such as a compressor or blower to mobilizeambient air (35), forming gas stream (43). Gas stream (43) istransported via a conduit such as a pipe, tube, or hose (38) to heater(39) and then to a manifold (40), where gas stream (43) is delivered viaa pipe, tubing, hose, or other conduit (41), to at least one aerationdevice (29) and then introduced into powder bed (24).

The relative locations of the optional manifold (40) and heater (39) areinsignificant, but the gas stream at the exit of aeration device (29)must be heated to at least the first predetermined transitiontemperature. The pressure control device (28) can be manual orautomated. In this embodiment, the pressure control device (28) ismanually adjusted to attain the desired pressure as indicated on thepressure indicator (27).

The following embodiments are provided as specific support and/orenablement for the appended claims. Accordingly, the present disclosureprovides:

E1. A method for manipulating crystal structure to fluidize a powdercomprising: collecting a powder comprising a crystal structure in avessel wherein the vessel comprises an exterior wall and an interiorvolume and wherein the powder forms a powder bed within the interiorvolume; injecting a heated compressed gas into the vessel by way of oneor more gas inlet ports; and agitating and heating the powder with theheated compressed gas to bring an average temperature of the powder toleast a predetermined transition temperature, so as to transform thecrystal structure of substantially all of the powder so that the crystalstructure is transmuted to facilitate an improvement in flowabilityrelative to the former crystal shape.

E2. The method of E1, wherein the injecting a heated compressed gas stepfurther comprises providing the heated compressed gas stream to at leastone aeration device in contact with the powder bed, wherein the at leastone aeration device is selected so as to evenly distribute the heatedcompressed gas stream throughout the powder bed.

E3. The method of E1, wherein the injecting a heated compressed gas stepfurther comprises pressurizing the heated compressed gas to apredetermined pressure by a gas handling system, the predeterminedpressure selected so as to facilitate the fluidization of the powderbed.

E4. The method of E1, further comprising controlling the temperature ofthe heated pressurized gas via a temperature control means comprising atleast one temperature sensing device and having a means by which tocontrol the temperature of the heated pressurized gas.

E5. The method of E1, further comprising controlling the pressure of thegas stream via a pressure control means comprising at least one pressuresensing device located in contact with the heated pressurized gas andpositioned upstream of the at least one gas inlet connection and havinga means for varying the pressure of the heated pressurized gas streamprior to the gas inlet connection.

E6. The method of E1, wherein the injecting a heated compressed gas stepfurther comprises establishing a heated pressurized gas stream flow ratesufficient to achieve initial fluidization of the powder bed byovercoming a first resistance to the heated pressurized gas stream flowinherent in the gas handling system and a second resistance to gas flowresulting from the structure of the powder bed wherein after achievinginitial fluidization of the powder bed, the heated pressurized gasstream flow rate is further adjusted to achieve stable fluidization ofthe powder bed without causing the powder to become entrained in the gasstream.

E7. The method of E1, wherein the agitating and heating the powder stepfurther comprises achieving stable fluidization of the powder byaltering the crystal structure of the powder.

E8. The method of E1, further comprising removing the heated pressurizedgas stream from the vessel via vessel at least one atmospheric vent.

E9. The method of E1, further comprising removing the agitated andheated powder from the vessel via an outlet portal.

Several variations in the implementation of the present invention havebeen described. The specific arrangements and methods described here areillustrative of the principles of this invention. Those skilled in theart may make numerous modifications in form and detail without departingfrom the true spirit and scope of the invention. Although this inventionhas been shown in relation to a particular embodiment, it should not beconsidered so limited. Rather it is limited only by the appended claims.

The invention claimed is:
 1. An apparatus for manipulating crystalstructure of a powder to improve flowability comprising: a vessel havinginsulation, a rigid exterior shell, an interior space having a bottom ofa predetermined capacity for storing a powder bed comprised of a powder,the powder having a temperature and a crystal structure, the vesselfurther having an inlet portal through which the powder enters theinterior space, and at least one atmospheric vent extending from theinterior space through the exterior shell of the vessel; a gas stream,provided to the powder bed, having a temperature and pressurized to apredetermined pressure by a gas handling system, the predeterminedpressure and temperature of the gas stream selected so as to aerate thepowder and achieve fluidization; at least one aeration device selectedfrom the group consisting of air slides, air pads, natural air stones,synthetic air stones, metallic stones, and pozzolanic stones, andinstalled within the interior space so as to be in contact with thepowder bed stored therein, the at least one aeration device having atleast one gas inlet connection extending beyond the exterior shell whichreceives the gas stream; wherein the at least one aeration device, ableto withstand the temperature of the gas stream, is selected so as toevenly distribute the gas stream to the powder bed to control thetemperature of the powder, to cause the powder to undergo a change inthe crystal structure of the powder and cause the powder bed to achievefluidization; a temperature control means for controlling thetemperature of the gas stream comprising at least one temperaturesensing device and a means by which to control the temperature of thegas stream, selected so as to control the temperature of the powder; apressure control means to control the pressure of the gas streamcomprising at least one pressure sensing device in contact with the gasstream and positioned upstream of the at least one gas inlet connectionand a means for varying the pressure of the gas stream prior to the gasinlet connection; and an outlet portal positioned below the inlet portalthrough which the powder exits the vessel, wherein the at least oneaeration device is positioned below the outlet portal.
 2. The apparatusof claim 1, wherein the crystal structure of the powder substantiallyincludes twinning below a first predetermined transition temperature andthe crystal structure of the powder does not include twinning above thefirst predetermined transition temperature.
 3. The apparatus of claim 1,wherein the first predetermined transition temperature is about 100degrees Celsius.
 4. The apparatus of claim 1, wherein the atmosphericvent comprises a bin vent filter open to the atmosphere, through whichthe gas stream exits the interior space.
 5. The apparatus of claim 1,wherein the gas stream is heated and pressurized ambient air.
 6. Theapparatus of claim 1, further comprising a fabric covering the at leastone aeration device.
 7. The apparatus of claim 1, wherein the powderfurther comprises sodium sulfate.
 8. The apparatus of claim 1, whereinthe temperature of the at least one aeration device is able to withstandis at least 220 degrees F.
 9. The apparatus of claim 1, wherein theaeration device is suspended above the bottom of the interior space ofthe vessel, below the outlet portal.
 10. The apparatus of claim 1,wherein the aeration device is positioned so as to be in contact withthe bottom of interior space of vessel, below the outlet portal.